Newest planets most Earth-like yet, NASA astronomers say

NASA's discovery of three new planets -- circling comfortably between fire and ice -- bring us closer to that most far-fetched of dreams: We may not be alone.

These newcomers to the growing planetary list are the most Earth-like in their location and size yet, buoying hopes that they might have atmospheres hospitable to life.

"The discovery represents a historic moment in science," said UC-Berkeley's Geoff Marcy, a member of the Kepler telescope team at NASA Ames Research Center, near Mountain View, that made the finding. "How long before we find Earth 2.0?"

This artist's concept provided by NASA April 18, 2013, depicts NASA's Kepler misssion's smallest habitable zone planet. Seen in the foreground is Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra. AFP PHOTO / HANDOUT / NASA Ames / JPL-Caltech / T. Pyle (T. PYLE)

They're too far away to visit, but they can be detected from Kepler's perch in space. Two of the planets orbit the star Kepler 62, slightly cooler than our sun and 1,200 light years distant in the constellation Lyra. The third orbits the sunlike star Kepler 69, in the constellation Cygnus 2,700 light years from earth.

The next step is to explore their atmospheres, looking for key elements.

"If they have CO2 or water, they can have life," said William Borucki, the principal investigator on the Kepler Mission. "If they have oxygen, maybe higher life."

Planet discoveries used to be special, but now they're as common as a cheap hotel. If each star has an average of five planets, and our galaxy holds 200 billion stars, perhaps a trillion planets are out there, awaiting discovery. So far, we've found 2,700.

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Most live in the wrong neighborhoods -- either too close or too far from their suns to hold life. If they're too near, they get blowtorched. If they're too distant, they're frigid. A few don't seem to circle at all, but have wacky orbits that eventually fling them from their star systems, as if from a slingshot.

The most unlucky planets don't have a home sun, but slide among the stars untethered by gravity.

The few "habitable zone" planets have been vast and gas enveloped, almost the size of Neptune or Jupiter. The previous record-holder in the habitable zone was Kepler-22b, nearly two and half times larger than Earth, Marcy said.

"That exoplanet is so large that it certainly is enshrouded in a large envelope of hydrogen gas and perhaps water," he said.

These new discoveries are special because they are prime real estate -- and they have enough gravity to keep their protective atmospheres, scientists said.

The new planets are:

Kepler 62-e: About 60 percent larger than Earth, and closer to its star, it may be hot and muggy, scientists say. Because of the force of gravity on a planet its size, "We could walk on that, although it would be difficult," said Borucki.

Relative sizes of Kepler habitable zone planets discovered as of April 18, 2013 in this artist's rendition provided by NASA. (L to R) Kepler-22b, Kepler-69c, Kepler-62e, Kepler 62f and Earth. Scientists using NASA's Kepler space telescope have found the best candidates yet for habitable worlds beyond the solar system officials said Thursday. REUTERS/NASA Amers/JPL-Caltech/Handout (HANDOUT)

Kepler 62-f: About 40 percent larger than Earth, it is the exoplanet closest to Earth size, and right in the middle of the habitable zone.

Kepler 69-c: The most distant and least understood planet. Scientists are uncertain about its composition, but they know that it is about 70 percent larger than Earth.

The discovery of the Kepler 62 planets was reported in Thursday's online issue of the journal Science. The Kepler 69 planet was announced in The Astrophysical Journal.

To learn more about planets closer to home, NASA will use its newly completed "Automated Planet Finder" telescope at Lick Observatory on Mount Hamilton. It will seek out Earth-like planets around the nearest stars, within 20 light years of us. Scientists hope to begin using it this summer.

"These habitable zone planets indicate that worlds with lakes and oceans number in the billions within our home Milky Way Galaxy," said Marcy. "Such planets can certainly spawn biology as we know it."

"The next great scientific question is even more daunting: How often does simple, single-cell life spring up on these habitable worlds?" he asked. "How common are intelligent critters who look up at their night sky asking the same questions about their uniqueness in the universe?"